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physics
electricity and magnetism

Questions and Answers of Electricity and Magnetism

Calculate the peak output voltage of a simple generator whose square armature windings are 660 cm on a side the armature contains 155 loops and rotates in a field of 0.200T at a rate of 120 rev/s.
Typical large values for electric and magnetic fields attained in laboratories are about 1.0 x 104 V/m and 2.0 T.(a) Determine the energy density for each field and compare.(b) What magnitude
What is the inductance L of the primary of transformer whose input is 220 V at 60.0 Hz if the current drawn is 5.8A? Assume no current in the secondary.
A 130-mH coil whose resistance is 18.5Ω is connected to a capacitor C and 1360-Hz source voltage. If the current and voltage are to be in phase, what value must C have?
And inductance coil draws 2.5-A de when connected to a 36-V battery. When connected to a 60-Hz 120-V (rms) source the current drawn is 3.8 A (rms). Determine the inductance and resistance of the coil.
A 1350-mH inductor with 2.0Ω resistance is connected in series to a 20-μF capacitor, and a 60-Hz, 45-V source calculate. (a) The rms current, and. (b) The phase angle.
The Q factor of a resonance circuit can be defined as the ratio of the voltage across the capacitor (or inductor) to the voltage across the resistor, at resonance. The larger the Q factor, the
What would be the advantage, in Faraday’s experiments (Fig. 21-1), of using coils with many turns?
What is the difference between magnetic flux and magnetic field? Discuss.
Suppose you are holding a circular ring of wise and suddenly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced in the wire? Is a current induced
Two loops of wire are moving in the vicinity of a very long straight wire carrying a steady current as shown in Fig 21-43. Find the direction of the induced current in each loop.
Suppose you are looking along a line through the centers of two circular (but separate) wire loops, one behind the other. A battery is suddenly connected to the front loop establishing a clockwise
In Fig, 21-44 determine the direction of the induced current in resistor RA when(a) Coil B is moved toward coil A,(b) When coil B is moved away from A.(c) When the resistance RE is increased.
In situations where a small signal must travel over a distance, a “shielded cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor
What is the advantage of placing the two insulated electric wires carrying as close together of even twisted about each other?
Explain why, exactly the lights may dim briefly when a refrigerator motor starts up. When an electric heater is turned on, the lights may stay dimmed as long as the heater is on. Explain the
Use Figs 21-15 and 21-17 plus the right-hand rules to show why the counter torque in a generator opposes the motion.
Will an eddy current brake (Fig. 21-20) work on a copper or aluminium wheel, or must the wheel be ferromagnetic? Explain.
It has been proposed that eddy currents be used to help sort solid waste for recycling. The waste is first ground into tiny pieces and iron removed with a de magnet. The waste then is allowed to
The pivoted metal bar with slots in Fig.21-45 falls much more quickly through a magnetic field than does a solid bar. Explain.
If an aluminium sheet is held between the poles of a large bar magnet, it requires some force to pull it out of the magnetic field even though the sheet is not ferromagnetic and does not touch the
A bar magnet falling inside a vertical metal tube reaches a terminal velocity even if the is evaluated so that there is no air resistance. Explain.
A metal bar, pivoted at one end, oscillates freely in the absence of a magnetic field, its oscillations are quickly damped out. Explain. (This magnetic damping is used in a number of practical
An enclosed transformer has four wire leads coming from it. How could you determine the ratio of turns on the two coils without taking the transformer apart? How would you know which wires paired
The use of higher-voltage lines in homes –say, 600 V or 1200 V-would reduce energy waste. Why are they not used?
A transformer designed for a 120-V ac input will often “burn out’ if connected to a 120-Vdc source. Explain.
How would you arrange two flat circular coils so that their mutual inductance was? (a) Greatest, (b) Least (without separating them by a great distance)?
Does the emf of the battery in Fig. 21-33 affect the time needed for the LR circuit to each (a) A given fraction of its maximum possible current, (b) A given value of current? Explain.
In an LRC circuit, can the rms voltage across (a) An inductor, (b) A capacitor lies greater than the rms voltage of the ac source? Explain.
Describe briefly how the frequency of the source emf affects the impedance of (a) A pure resistance, (b) A pure capacitance. (c) A proc inductance. (d) An LRC circuit near resonance (R small), (e) An
Describe how to mate the impedance in an LRC circuit a minimum.
The electric field in an EM wave travelling north oscillates in an east-west plane. Describe the direction of the magnetic field vector in this wave.
Is sound an electromagnetic wave? If not, what kind of wave is it?
Can EM waves travel through a perfect vacuum? Can sound waves?
When you flip a light switch on, does the light go on immediately? Explain.
Are the wavelengths of radio and television signals longer or shorter than those detectable by the human eye?
When you connect two loudspeakers to the output of a stereo amplifier, should you be sure be a time lag between speakers? Explain.
In the electromagnetic spectrum, what type of EM wave would have a wavelength of 103 km? 1 km? 1 m? 1 cm? 1mm? 1 μm?
Can radio waves have the same frequencies as sound waves (20Hz-20,000Hz)?
Can two radio or TV stations broadcast on the same carrier frequency? Explain.
If a radio transmitter has a vertical antenna, should a receiver’s antenna (rod type) be vertical or horizontal to obtain best reception?
The carrier frequencies of FM broadcasts are much higher than for AM broadcasts. On the basis of what you learned about diffraction in Chapter 11, explain why AM signals can be detected more readily
Discuss how cordless telephones make use of EM waves. What about cell phones?
A lost person may signal by flashing a flashlight on and off using Morse code. This is actually a modulated EM wave. Is it AM or FM? What is the frequency of the carrier, approximately?
At a given instant, a 1.8-A current flows in the wires connected to a parallel-plane capacitor. What is the rate at which the electric field is changing between the plates if the square plates are
A 1200-nF capacitor with circular parallel plates 2.0 cm in diameter is accumulating charge at the rate of 35.0 mC/s at some instant in time. What will be the magnitude of the induced magnetic field
If the magnetic field in a travelling EM wave has a peak magnitude of 17.5 nT at a given point, what is the peak magnitude of the electric field?
In an EM wave traveling west, the B field oscillates vertically and has a frequency of 80.0 kHz and rms strength of 6.75 x 10-9 T. what are the frequency and rms strength of the electric field, and
What is the frequency of a microwave whose wavelength is 1.60 cm?
What is the wavelength of a 29.75 x 109 -Hz radar signal?
An EM wave has frequency 9.66 x 1014 Hz. What is its wavelength, and how would we classify it?
An EM wave has a wavelength of 650 nm. What is its frequency, and how would we classify it?
How long does it take light to reach us from the Sun 1.50 x 108 km away?
A widely used “short-wave” radio broadcast band is referred to as the 49-m band. What is the frequency of a 49-m radio signal?
Our nearest star (other than the Sun) is 4.2 light-years away. That is, it takes 4.2 ears for the light it emits to reach Earth. How far away is it in meters?
A light-year is a measure of distance (not time). How many meters does light travel in year?
How long would it takes a message sent as radio waves from Earth to reach Mars(a) when nearest Earth,(b) When farthest from Earth?
What is the minimum angular speed at which Michelson’s eight-sided mirror would have had to rotate to reflect light into an observer’s eye by succeeding mirror faces?
A student wants to scale down Michelson’s light-speed experiment to a size that will fit in one room. A six sided mirror is available, and the stationary mirror can be mounted 12 m from the
Who will hear the voice of a singer first- a person in the balcony 50.0 m away from the stage (Fig.22-19), or a person 3000 km away at home whose ear is next to the radio? How much sooner? Assume
Pulsed lasers used in science and medicine produce very short bursts of electromagnetic energy. If the loser light wavelength is 1062 nm (this corresponds to a Neodymium-YAG laser), and the pulse
The E field in an EM wave in free space has a peak of 21.8 mV/m. What is the average rate at which this wave carries energy across unit area per unit time?
The magnetic field in a traveling EM wave has an rms strength of 28.5 nT. How long does it take to deliver 235 J of energy to 1.00 cm2 of a wall that it hits perpendicularly?
How much energy is transported across a 1.00-cm2 area per hour by an EM wave whose E field has an rms strength of 38.6 V / m?
A spherically spreading EM wave comes from a 1200-W source. At distance of 10.0 m, what is the average intensity, and what is the rms value of the electric field?
A 12.8-m W laser puts out a narrow beam 1.75 mm in diameter. What are the average (rms) values of E and B in the beam?
Estimate the average power output of the Sun, given that about 1350 W/m2 reaches the upper atmosphere of the earth.
If the amplitude of the B field of an EM wave is 2.5 x 10-7, (a) What is the amplitude of the E field?(b) What is the average power per unit area of the EM wave?
(a) What is the amplitude of the E field?(b) What is the average power per unit area of the EM wave?
Estimate the radiation pressure due to a 100-W bulb at a distance of 8.0 cm from the center of the bulb. Estimate the force exerted on your fingertip if your place it at this point.
What is the range of wavelength for? (a) FM radio (88 MHz to 108 MHz) and (b) AM radio (535 kHz to 1700 kHz)?
Estimate the wavelength for 1.9-GHz cell phone reception.
Compare 940 on the AM dial 94 on the FM dial. Which has the longer wavelength, and by what factor is it larger?
What are the wavelengths for two TV channels that broadcast at 54.0 MHz (Channel 2) and 806 MHz (channel 69)?
The variable capacitor in the tuner of an AM radio has capacitance of 2800 pF when the radio is tuned to a station at 550 kHz. What must the capacitance be for a station near the other end of the
The oscillator of a 96.1-MHz FM station has a inductance of 1.8 μH. What value must the capacitance be?
A certain FM radio tuning circuit has a fixed capacitor C = 840 pF. Tuning is done by a variable inductance. What range of values must the inductance have to tune stations from 88 MHz to 108 MHz?
An amateur radio operator wishes to build a receiver that can tune a range from 14.0 MHz to 15.0 MHz a variable capacitor has a minimum capacitance of 82 pF. (a) What is the required value of the
A satellite beams microwave radiation with a power of 10 kW toward the Earth’s surface. 550 km away. When the beam strikes Earth, its circular diameter is about 1500 m. Find the rms electric field
A 1.60-m-long FM antenna is oriented parallel to the electric field of an EM wave. How large must the electric field be to produce a 1.00-m V (rms) voltage between the ends of the antenna? What is
If the Sun were to disappear or somehow radically change its output, how long would it take for us on Earth to learn about it?
Light is emitted from an ordinary lightbulb filament in wave-train bursts about 10-8 s in duration. What is the length in space of such wave trains?
(a) How long did it take for a message sent from Earth to reach the first astronauts on the Moon?(b) How long will it take for a message from Earth to reach the first astronauts who arrive on Mars;
A radio voice signal from the Apollo crew on the Moon (Fig.22-20) was beamed to a listening crowd from a radio speaker. If you were standing 25 m from the loud speaker, what was the total time lag
Cosmic microwave background radiation fills all space with and average energy density of 4 x 10-14 J/m.(a) Find the rms value of the electric field associated with this radiation. (b) How far from a
What are Eo and Bo 2.00 m from a 95- W light source? Assume the bulb emits radiation of a single frequency uniformly in all directions.
Estimate the rms electric field in the sunlight that hits Mars, knowing that the Earth receives about 1350 W / m2 and that Mars is 1.52 times farther from the Sum (on average) than is the Earth.
At a given instant in time, a traveling EM waves is noted to have its maximum magnetic field pointing west and its maximum electric field pointing south. In which direction is the wave traveling? If
Estimate how long an AM antenna would have to be if it were. (a) ½ λ or. (b) ¼ λ. AM radio is roughly 1 MHz (530 kHz to 1.7 MHz).
How large an emf (rms) will be generated in an antenna that consists of a 380-loop circular coil of wire 2.2 cm in diameter if the EM wave has a frequency of 810 kHz and is transporting energy at an
The average intensity of a particular TV station’s signal is 1.0 x 10-13 W/m2 when it arrives at a 33-cm-diameter satellite TV antenna. (a) Calculate the total energy received by the antenna during
15 km from a radio station’s transmitting antenna, the amplitude of the electric field is 0.12 V / m .What is the average power output of the radio station?
The variable capacitance of a radio tuner consists of six plates connected together placed alternately between six other plates, also connected together (Fig. 22-21). Each plate is separated from its
A radio station is allowed to broadcast at an average power not to exceed 25 kW. If an electric field amplitude of 0.020 V/m is considered to be acceptable for receiving the radio transmission,
A point source emits light energy uniformly in all directions at an average rate Po with a single frequency f. Show that the peak electric field in the wave is given by
Suppose a 50-kW radio station emits EM waves uniformly in all directions (a) How much energy per second crosses a 1.0-m2 area 100 m from the transmitting antenna?(b) What is the rms magnitude of the
Repeat Problem 52 for a distance of 100 km from the station.
What is the maximum power level of the radio station of Problem 52 so as to void electrical breakdown of air at a distance of 1.0 m from the antenna? Assume the antenna is a point source. Air breaks
If you charge a pocket comb by rubbing it with a silk scarf, how can you determine if the comb is positively or negatively charged?
Why does a shirt or blouse taken from a clothes dryer sometimes cling to your body?

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